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Tachysphex pechumani, the antenna-waving wasp, has a disjunct geographic distribution in the Lower Peninsula of Michigan, Indiana Dunes, Oak Openings of Ohio, southern Ontario, and New Jersey pinelands. This distribution is tied to excessively/well-drained sandy soils, oak/pine-dominant barrens, savanna and woodland, climate moderation related to proximity to large bodies of water, habitat fragmentation from natural causes and human disturbance, and 20th-century land preservation. The 550-km gap between subpopulations in southwestern Ontario and southern New Jersey may be the consequence of Early Holocene pine-dominant barrens, savanna, and woodland being supplanted by deciduous and deciduous-coniferous forest on loamy sand in the northeastern United States during the past 6000 years. A plausible scenario as to where T. pechumani lived during the past 18,000 years and what dispersal route(s) enabled it to attain its current geographic distribution is presented.
A re-examination of the nesting behavior of T. pechumani from 1991 to 1999 at 43 sites in the central Great Lakes Region and southern New Jersey revealed little difference between the two groups. More than 200 females were observed nesting solitarily in June–July in sandy soils of mostly oak/pine-dominant barrens, savanna, and open woodland. Tachysphex pechumani was univoltine, with a flight period encompassing mainly late spring–early summer. Emergence and senescence of wasps occurred earlier in the southern and later in the northern parts of the species' range. Males were not territorial and dug resting burrows for the night and to avoid the hot sand and inclement weather. Nesting aggregations ranged from a few to 48 females at a site. Distinct bimodality in nesting occurred on hot days, with peak activity in late morning and a secondary rise in activity in mid- to late afternoon. Wasps demonstrated genus-atypical burrow excavation and tumulus formation. Rather slow and jerky movements characterized female behavior. There was little variation among females in burrow excavation, orientation, hunting, prey capture, prey transport, and final closure. Geographic variation included longer burrows and deeper cells at many southerly locations. Females preyed mostly on nymphal Melanoplinae and Gomphocerinae (Acrididae), primarily Melanoplus species. Some Melanoplus species were captured earlier in the season than Gomphocerinae in synchrony with their earlier emergence and growth schedules. Wasps faced and circled prey while waving antenna before pouncing on and stinging the grasshopper. The relatively large prey was often transported to the nest slowly and haltingly. Random positioning of paralyzed grasshoppers near entrances constituted genus-atypical behavior. A single paralyzed prey was placed commonly head inward and ventral side upward in the one-celled nest. The wasp's egg was laid transversely across the grasshopper's pro- and mesosternum. Some females completed two nests per day under favorable weather conditions. Sarcophagid flies of the tribe Miltogrammini (Sphixapata rubriventris, S. vigilans, S. trilineata, Sphenometopa tergata, Taxigramma heteroneura) were major enemies of this wasp.
This study addressed aspects of the ecology of Tachysphex pechumani (antenna-waving wasp), a rare solitary wasp. Wasps nested in compacted sand, primarily where vegetative cover was 5–30% and vegetation height was 0.5 to 33 cm. Miltogrammine flies and predators presented challenges to wasp success at the study sites. The timing and duration of T. pechumani's breeding season conformed to an apparent abundance peak of acridid grasshopper nymphs used by wasps, based on sweep-net data. Heat increased wasp activity to an upper threshold of 56 °C at the sand surface, at which temperature wasps ceased working. Weak flying abilities of both sexes suggested that populations were effectively isolated and vulnerable to habitat loss or fragmentation. Management for wasps should include maintenance of open sites and prohibition of sand disturbance.